Glass fiber filtration media with at least two different fiber diameters

ABSTRACT

A method of forming filtration media, and the media so formed. The media has glass fibers of at least two substantially different diameters, such as 18 microns and 21 microns. Each of the glass fibers is continuous throughout the media and is substantially the same diameter along its entire length. The fibers can be made using a bushing plate in the Modigliani process in which the plate has orifices of at least two different sizes. The fibers made thereby have two different sizes, thereby resulting in a filtration media superior to conventional media, despite having a similar amount of glass and no more weight.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/625,028 filed Nov. 4, 2004.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

(Not Applicable)

REFERENCE TO AN APPENDIX

(Not Applicable)

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to filtration media, and morespecifically to glass fiber filtration media.

2. Description of the Related Art

A known method for making fiberglass is described in several patents toModigliani: U.S. Pat. Nos. 2,546,230; 2,609,320; and 2,964,439 areincorporated herein by reference. These patents disclose an apparatus inwhich a slowly reciprocating, melting furnace feeds molten glass throughspinning orifices which discharge an array of fine, continuous glassfilaments or fibers that are wrapped circumferentially around a rapidlyrotating drawing drum. The melting furnace uses a bushing plate withorifices of the same size, through which the molten glass flows, to formthe glass fibers.

The melting furnace reciprocates relatively slowly in a longitudinaldirection above the drum's rapidly rotating circumferential surface,thereby forming a build-up of layers of continuous fibers oriented atacute angles with one another. During winding of the fibers on therotating drum, a binder, such as a thermosetting resin, is commonlyapplied by spraying the fibers already deposited on the drum to bind thefibers at their overlapping junctions with fibers of previouslydeposited layers.

After a suitable thickness of fibers has been created, the condensed matis removed from the drum by slitting the mat longitudinally and parallelwith the axis of the drum. The condensed mat can be modifiedsubsequently by being deposited on a conveyor belt that moves at a veryslow rate. The condensed mat is generally rectangular in shape, and thefibers in the mat extend, due to the orientation of the rectangular maton the conveyor, substantially completely across the width of the matand substantially perpendicular to the direction of movement of theconveyor belt. At the exit end of the conveyor belt, a retarding rollerpresses the condensed mat against the conveyor belt, which is supportedby an oppositely rotating support roller. The leading end of thecondensed mat beyond the retarding roller is stretched or expandedlongitudinally up to hundreds of times its original, condensed length.The expanding is a continuous process with the leading end being pulledlongitudinally while the retarding roller/support structure minimizesthe forward movement of the remaining length of the condensed mat.

As the mat expands longitudinally, it also expands (“fluffs”) in thedirection of the mat's thickness to a consistency resembling cottoncandy. Additionally, during the expansion of the mat, the fibers thatare originally oriented transversely to the direction of movement arepulled longitudinally, thereby tending to rotate and reorient the fibersto a 45 degree or greater angle with respect to the longitudinaldirection. During the expansion process, in which the original matincreases in length enormously and “fluffs” to a significantly greaterthickness, the mat necks down to a smaller width. Such an expandedproduct can be used for filtration purposes, such as by attaching theproduct to a frame.

As an alternative to using the product as a filtration media, theproduct can be compressed into a dense mat to use as a fibrousreinforcement, for example, in pultruded composite products. After themajority of the expanding takes place, the fluffed, expanded mat can becompressed in the direction of its thickness by rolling, and it isheated by radiant heaters to set the thermosetting resin incorporatedduring the winding of the fibers on the drum. Thereafter, the stretchedglass fiber mat is wound on a spool. Thus, the compressed mat, which ismuch longer than the original, condensed mat, is a continuous strandfiberglass mat, because the condensed mat from which it is derived wasformed from continuous strands of glass.

As noted above, the glass-melting furnace of the Modigliani processmachine feeds molten glass through orifices that are formed in a bushingplate. The bushing plate is a flat plate, normally made of a metalalloy, through which holes are formed and through which molten glassflows during use. The size of each orifice has a direct effect on thediameter of the fibers formed thereby. Conventionally, bushing plateholes are all the same size in order to avoid temperature gradients thatare present if different size fibers were used. The process of formingfibers can thus be “tuned” to the exact characteristics desired withouthaving to compensate for a plurality of fiber diameters, and therefore,fiber characteristics. The orifices in the bushing plates are alldrilled to a size that results in a particular fiber size. Therefore, aparticular drill size results, according to conventional technology, ina particular finished fiber size.

The Applicant is aware of the use of a bushing plate with orifices oftwo different sizes to form a condensed glass fiber mat using theModigliani process. The condensed mat was expanded and then compressedinto a thin mat in the conventional manner and sold for use inpolymer-reinforced composites. The sale of this compressed mat hasoccurred for several years. The fibers in this mat were between 28 and40 microns in diameter, and the compressed mat had a thickness ofapproximately one-quarter inch. The characteristics of this mat make itunsuitable for use as a filtration media.

It is also known to be conventional for filtration media to havedifferent fiber diameters, but only within layers of a multi-layer web.This is accomplished by laying fibers in separate layers, and making onelayer with fibers of one size, and another layer with different fibersof a different size. Furthermore, fibers made using the Modiglianiprocess can change each fiber's size during manufacture, for example byrotating the drawing drum faster, which produces a layer of one sizefiber, and then rotating the drum slower, which produces another layerof a larger size fiber. For example, one can operate at a first drumspeed, and, for example, get a 30 micron fiber, and then decrease thespeed to get a 36 micron fiber. However, in all of the prior art, thefibers in each layer are the same diameter, even after expansion of theoriginal mat.

BRIEF SUMMARY OF THE INVENTION

The invention is a method of making a filter. The method comprisesextruding molten glass through a plurality of orifices formed in aplate. This forms a plurality of glass fibers, and each of the fibersextends from a corresponding one of the orifices. Furthermore, each ofthe plurality of orifices has one of at least two substantiallydifferent orifice diameters. In one embodiment, there are first andsecond fiber diameters in a range between about 17 microns and about 26microns, and in one particular embodiment, the first diameter is about18 microns and the second diameter is about 21 microns.

The fibers are wrapped around a rotating drawing drum to form acondensed mat, and the mat is removed from the drawing drum. The mat isexpanded, such as by pulling on opposite sides thereof, thereby formingthe filtration media through which gas can flow. The filtration media isthen mounted in a filter frame, such as a disposable frame or thepermanent frame of a gas duct.

The invention also contemplates a filtration media made of a pluralityof continuous glass fibers, where each of the fibers has one of at leasttwo substantially different diameters. Furthermore, each fiber'sdiameter is substantially the same throughout the filtration media. Thefiltration media is contemplated to have first and second diameters in arange between about 17 microns and about 26 microns, where the firstdiameter is about 18 microns and the second diameter is about 21microns. The filtration media can be mounted in a gas flow path forremoving particulate from gas flowing through the filtration media.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view in perspective illustrating a bushing plate havingorifices of two sizes.

FIG. 2 is a magnified schematic view illustrating filtration media madeaccording to the present invention.

FIG. 3 is a table showing the MERV, pressure drop and particle sizeefficiency values for three samples tested in experiments to ascertainthe advantages of the present invention over the prior art.

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific term so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose. For example, theword connected or term similar thereto are often used. They are notlimited to direct connection, but include connection through otherelements where such connection is recognized as being equivalent bythose skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention uses a bushing plate10, shown in FIG. 1, having orifices of at least two different sizes. Inone embodiment, the smaller orifices 12 are formed by a size 25 drillresulting in an orifice diameter of 0.1495 inches, which forms fibershaving a diameter in the range of about 16 to 22 microns, with anaverage fiber diameter of about 19 microns. The larger orifices 14 areformed using a size 22 drill resulting in an orifice diameter of 0.1570inches, which forms fibers having a diameter in the range of about 26 to32 microns, with an average fiber diameter of about 29 microns. Ofcourse, the particular diameters noted herein are not the only orificediameters. Other orifice sizes are contemplated, and will be apparent tothe person having ordinary skill upon examining the description herein.

The orifices are formed in rows within a rectangular region on thebushing plate 10 shown in FIG. 1. The orifices of different sizealternate along each row. Therefore, each orifice 12 of a smaller sizehas only larger size orifices 14 closest to it, and vice versa.

Other contemplated embodiments can have three, four or moredifferent-sized orifices in the same bushing plate, and it iscontemplated that the orifices will be alternated as much as possible onthe plate. It is contemplated that these orifices can range in sizesufficient to form fibers in the range from about 17 microns to about 26microns in diameter.

The bushing plate 10 is used in the conventional Modigliani process forforming a mat, and then expanding the mat to form filtration media thatis used in filters. Thus, the bushing plate 10 is mounted beneath afurnace of molten glass that is directed through the orifices 12 and 14to form cooled glass fibers that are drawn around a rotating drawingdrum. These fibers form overlapping layers in a condensed mat that isthen slit and removed from the drum.

The mat formed is then expanded in the conventional manner, such as bypulling on opposing ends so that the fibers change relativeorientations, which causes the fibers to “fluff up.” This expansionresults in a filtration media that is slightly narrower, andsignificantly thicker, than the original condensed mat, but which canhave one of many different thicknesses as will become apparent to aperson of ordinary skill. A contemplated thickness is about one inch,because this is common for residential HVAC filtration. Differentthicknesses are necessary for different applications.

The mat formed by the bushing plate 10, and, therefore, the resultingfiltration media, has larger fibers alternating with smaller fibers asshown schematically in FIG. 2. The fibers in FIG. 2 have twosubstantially different sizes, and the sizes and differences should beconsidered exaggerated for illustrative purposes. The filtration mediawith these different fiber diameters is placed in a frame, such as adisposable cardboard frame, and air is forced through it. When thisoccurs, the smaller and larger fibers provide advantageous filtrationcharacteristics, as shown by experimental results shown in FIG. 3. InFIG. 3, Sample 1 is the filter made according to the invention, Sample 2is a pleated synthetic fiber filter and Sample 3 is a conventionalunpleated glass fiber filter. Both Sample 2 and Sample 3 have one fiberdiameter throughout, as is conventional. The results show that theefficiency rating, which is denoted as the Minimum Efficiency ReportingValue (MERV) obtained according to the well-known ASHRAE test 52.2, ishigher for filtration media made according to the invention than withsynthetic pleated and conventional glass fiber filters. This occurswhile the invention has a smaller pressure drop than the pleated filter,and higher maximum particle size removal efficiency than both otherfilters.

It is theorized that the reason the filtration media made according tothe invention is advantageous is that small cavities are formed in thatcause the media to hold solid particles better than prior art filters.It is theorized that due to the size differences in the fibers, theorifices throughout the media may vary widely; i.e., the orifices havegreater variations in size than in conventional filters. This could aidin holding particles of various sizes, and thereby produce superiorresults.

With the present invention, it is preferred that each of the fibers hasthe same diameter throughout the entire filter media. Thus, becausethere are different diameter fibers throughout the entire thickness, thefibers have different fiber diameters within every “layer” of the media.The filter of the present invention is different from conventionalmedia, therefore, inasmuch it has two different sizes throughout theentire filter.

One application of the invention is in paint and gel coat filtration.For example, in the composite industry boats are commonly manufacturedusing a “spray up” process, where filters capture the over-sprayedresin. The present invention is particularly suited to this application.Of course, there are applications for this product in other industries,such as in residential heating, ventilation and air conditioning (HVAC)systems, industrial HVAC filtration, and others that will becomeapparent to a person of ordinary skill from this description.

It is contemplated that the filter media made according to the inventioncan be made in a process other than the Modigliani process. For example,in any process in which molten glass is extruded or otherwise forced,such as by gravity, through small orifices to form fibers, the presentinvention can be used. Thus, any structural body in which orifices areformed to pass glass through can have the plurality of different-sizedorifices. The bushing plate is not the only such structure that willwork.

While certain preferred embodiments of the present invention have beendisclosed in detail, it is to be understood that various modificationsmay be adopted without departing from the spirit of the invention orscope of the following claims.

1. A method of making a filtration media, the method comprising: (a)forcing molten glass through a plurality of orifices formed in a body toform a plurality of glass fibers, wherein each of said glass fibersextends from a corresponding one of said orifices and each of saidorifices has one of at least two substantially different orificediameters, thereby causing each of said glass fibers to have one of atleast two substantially different diameter; (b) wrapping said glassfibers around a rotating drawing drum to form a condensed mat; (c)removing the condensed mat from the drawing drum; (d) expanding themat's exterior dimensions, thereby forming filtration media.
 2. Themethod in accordance with claim 1, further comprising the step ofdirecting a flow of gas through the filtration media for removingparticulate from the gas.
 3. A product produced according to the processof claim
 1. 4. A filtration media made of a plurality of continuousglass fibers, each of said fibers having one of at least twosubstantially different diameters, and wherein each fiber's diameter issubstantially the same throughout the filtration media.
 5. Thefiltration media in accordance with claim 4, wherein said at least twosubstantially different diameters further comprise first and seconddiameters in a range between about 17 microns and about 26 microns. 6.The filtration media in accordance with claim 5, wherein the firstdiameter is about 18 microns and the second diameter is about 21microns.
 7. The filtration media in accordance with claim 5, wherein thefiltration media is mounted in a gas flow path for removing particulatefrom gas flowing through the filtration media.
 8. The filtration mediain accordance with claim 5, wherein the thickness of the filtrationmedia is about one inch.
 9. A method of making filtration media, themethod comprising (a) disposing a container of molten glass above arotating drawing drum; (b) forcing molten glass through a plurality oforifices formed in a body beneath the container to form a plurality ofglass fibers, wherein each of said glass fibers extends from acorresponding one of said orifices and each of said orifices has one ofat least two substantially different orifice diameters thereby causingeach of said glass fibers to have one of at least two substantiallydifferent diameters; (c) reciprocating the container while wrapping saidglass fibers around the rotating drawing-drum to form a condensed mat;(d) removing the condensed mat from the drawing drum; (e) applying atensile force to at least one edge of the mat for expanding the mat'sexterior dimensions.